A variety of batteries employing active metal anodes are known. Illustrative of batteries of this kind in the prior art are those disclosed, for example, in U.S. Pat. Nos. 3,514,337; 3,536,532; 3,700,502 and 3,892,590. A variety of electrolytes can be used in the fabrication of these systems.
It is recognized by those skilled in the art, that the discharge performance of non-aqueous cells containing an active metal anode can be significantly affected by the purity of the solvent and/or electrolyte solution. The presence of even trace impurities can adversely affect the performance and stability of the battery system. Transition metals or metal salt impurities such as nickel, iron, and copper or any electroactive compound can produce a variety of reduced or oxidized species This can result in self-discharge (poor shelf life) and poor voltaic performance of the cell. Numerous methods have been proposed to remove these impurities, however, most known prior attempts are time consuming and expensive Typical of known methods seeking to eliminate impurities include galvanostatic pre-electrolysis; various distillation techniques, e.g., vacuum distillation, atmospheric distillation and spinning band distillation, treatment with absorbants, such as activated carbon or alumina; and fractional crystallization. Frequently, it is necessary to use combination of the above techniques in an effort to obtain a solvent of suitable purity for use in non-aqueous cells.
It is the purpose of this invention, accordingly, to disclose a simple relatively practical and efficient process for removing such metal/metal salt impurities from organic solvents and/or electrolyte systems which are to be used for the fabrication of various non-aqueous cells